The availability of a high-energy heavy-ion beam from the Bevalac makes it possible to determine the effects of relatively well defined whole body high LET radiation. RF/J mice have been exposed to a fully stripped neon beam (400 MeV/amu) and will be observed for life shortening and leukemia induction. The relative biological effectivenesss (RBE) for a number of biological systems will also be investigated for this Neon beam, which has a mean LET of approximately 30 KeV per micron. We shall determine the RBE for bone marrow stem cells irradiated in vitro and in vivo for the plateau protion of the beam, and in vitro for the Bragg Peak region. We also plan to extend our observations concerning the RBE for interphase death of lymphocytes. The next project then will be to measure the RBE for jejunal crypt cell survival and for acute gastrointestinal death in mice.